As starting material for such glass bodies usually glass tubes or also glass rods having a circular profile may be used, which are then deformed or shaped to the desired profile in a hot malleable state.
DE 545 449 A discloses an apparatus for deforming or shaping glass tubes to glass tubes having a non-circular profile, wherein the glass tubes are conveyed through a nip while being in a heated state. An adjustment of squeezing rollers forming the nip during the shaping process is not disclosed. DE 1007962 A discloses a corresponding method for shaping glass tubes to thin insulating tapes or insulating layers.
JP 2006315919 A discloses an apparatus for shaping glass tubes to glass tubes having a non-circular profile. The positions of the squeezing rollers forming the nip can be adjusted for adjusting the profile of the glass tube after the shaping (deforming) process. An adjustment of the squeezing rollers forming the nip during the shaping process is not disclosed.
In order to accomplish a predetermined profile by deforming glass tubes, DE 19856892 A1 proposes to continuously measure the diameter and the wall thickness of the glass tube after the shaping process and to control or regulate an overpressure to be applied to the interior of the glass tube. An adjustment of the squeezing rollers forming the nip during the shaping process is not disclosed.
DE 102006015223 B3 of the Applicant discloses a method and an apparatus for producing a glass tube having a profile that differs from a circular profile. Here, the initial glass tube having the initial profile (so-called preform) first passes through a hot zone while forming of a drawing bulb and then passes a nip formed by a pair of rollers, where the drawing bulb is shaped (deformed) to a glass tube having a different profile. This shaping process is actually a process for re-drawing of the initial glass tube. During the re-drawing process, the positions of the squeezing rollers forming the nip in the direction of drawing the glass tube and/or in a direction perpendicular thereto can be adjusted. This adjustment of the positions of the squeezing rollers is for the purpose of achieving a constant profile of the glass tube after the shaping process. For this purpose, the profile of the glass tube after the shaping process may also be measured and used as a parameter for controlling or regulating. However, the adjustment of the positions of the squeezing rollers is not continuous in the sense of the present application, as disclosed below. Particularly, this adjustment is not performed such that a contact area between the respective squeezing roller and the hot glass tube in the shaping area is varied continuously.
Even if the initial glass tube is produced with high precision, the general conditions during the shaping process and the fluctuations of such general conditions lead to a precision that is not satisfactory for applications requiring a high geometric accuracy.